Methods currently used for particle size determination include counting methods, both optical and electrical, sedimentation methods, separation methods and surface measurement methods. Whilst such methods can be used to make reasonably accurate determinations of particle sizes, they are not generally suitable for use alongside industrial processes. They are either time consuming and tedious to perform, or depend upon the use of complicated and sophisticated apparatus and techniques. They also depend to a large degree upon inherent characteristics of the materials under test, such as density, so that they are of limited use with non-homogeneous particulate mixtures.